The measurement of tidal volumes in spontaneously breathing children during general anaesthesia using a Haloscale infant Wright respirometer.

The accuracy of tidal volume measurements made with a Wright Haloscale infant respirometer in children breathing spontaneously during general anaesthesia was assessed by a bench test. The tidal volumes and peak flow rates of 20 spontaneously breathing, anaesthetised children were measured with a pneumotachograph before and during surgery, and similar volumes, at the same flow rates, were delivered by a calibrated syringe simultaneously to the respirometer and a pneumotachograph. The results reveal that the mean (+/- s.d.) peak gas flow rates of children aged 6 years and less, 7.5 (+/- 1.6) and 9.3 (+/- 0.1) l/min before surgery and during surgery respectively, are significantly less than the peak flow rates, 11.3 (+/- 1.0) and 11.9 (+/- 1.5) before and during surgery, respectively, of children aged more than 6 years; and that the respirometer underestimates tidal volume by 10% when the peak flow rate is 11 l/min, and the percentage error in tidal volume estimation by the respirometer increases as the peak gas flow declines below 10 l/min.